United Kingdom Patent No. 1559679 and Application No. 2091003 disclosed how a sensor may be used to determine the proximity of sealing systems in rotary regenerative air pre-heaters and how to adjust the gap (or the extent of contact) in them using magnetic drive means controlled from those sensors.
The sensors in those prior documents are mounted on moving hoods of a stationary matrix regenerator. This brings a difficulty with it. The signals are of low amplitude and they have to be transmitted through contacts such as a slip ring between the rotating hood and the stationary parts of the device. The regenerators work in very hostile environments and because of this and the low amplitude of the signals we have found that unless very special care is taken with the design of the slip rings the noise level in the signal is unacceptably high and may result in erractic functioning of the magnetic drive.